The “Skinny” on our Metabolism

Does our metabolism slow as we age, and what can we do about it?

Getting older (and wiser) can come with plenty of benefits and positive experiences. By creating a healthy and vibrant lifestyle for ourselves, there is no question that we can age with grace. But is its inevitable that no matter what we do our metabolism will decrease with age? I have heard it many times before, “Doc, I just can’t lose the weight. I have always had a slow metabolism and it has just gotten worse with age.” This is a loaded statement, with some truth and some fiction. Hopefully this blog will help separate partial fact from partial fiction, but first, let’s start with definitions.

“Metabolism” is basically the process by which our bodies convert what we eat and drink into energy. Ingested calories are combined with oxygen to release the energy that our bodies need to function. When someone uses the term “metabolism,” they are usually referring to the Basal Metabolic Rate (BMR). The BMR accounts for 60-70% off all calories that we burn during the day (the others are thermogenesis and daily activity, more on this later). It is also referred to as the Basal Energy Expenditure (BEE). It is meticulously measured after 8 hours of sleep, a 12 hour fast, and the while lying still in a dark room where the oxygen you consume and the CO2 you expel is precisely measured. This is a true basal rate as you are not permitted to MOVE!

The resting metabolic rate (RMR) or resting energy expenditure (REE), is a less restrictive measurement that allows normal simple activities and will almost always be higher than the BMR. They are frequently used interchangeably even though there are some small but important differences as I mentioned.

Now let’s get into the main questions surrounding our metabolism:

Does BMR decrease with age? Yes and no. Basically yes, but there is a healthy debate about whether it is truly age related or if it is due to the decreased lean body mass (LBM) and increased fat mass that normally occurs as we age. There are plenty of studies out there about how the metabolic rate decreases by 2% every decade after age 25, or 5% every decade after age 40. A small proportion of that is likely due to age itself, but the greater association has been linked to loss of LBM. This is obviously important when it comes to treatment. We can’t reverse our age, but we can try to increase out LBM.

Does a lower BMR lead to weight gain? Yes it can. It does not by definition lead to weight gain. But it does make it more difficult to avoid weight gain. All it really means is that your body does not burn as many calories at rest as it once did. This is likely true also for burning calories with activity. To counter act this, you would need to burn more calories by exercising more and eating less, two things that are very difficult for the majority of the population.

What else can slow BMR?

1-There is certainly a genetic component. Some people are just born with a higher metabolic rate, and we are usually jealous of these people. But again, is it all in their BMR? Or are they also more energetic, exercising more and maintaining a higher LBM? Again, both genetics and activity level likely contribute equally.

2-Endocrine dysfunction- Hypothyroidism is the most often cited medical cause of decreased BMR. There is some debate in the literature, without a clear answer, if it is the cause or the effect. Are hypothyroid patients less active because they feel fatigued and lousy, and therefore exercise less, have lower LBM and lower BMR? Or does the hypothyroid condition itself directly lower the BMR? Chicken or the egg? Either way, the treatment is virtually the same. Treat the hypothyroidism, get them moving and exercising, and educate them on proper nutritional choices.

3- Weight and body composition. This is a particularly cruel problem. People with higher body fat have a lower BMR. People with higher body fat also on average tend to have more difficulty maintaining a regular exercise program, and need to work “harder” than someone with a lower body fat to reach the same BMR. It does seem a little unfair that a gym rat with high LBM burns more calories per unit of work than someone with a higher fat mass. Fair or not, that is the way our bodies are wired, and we need to adapt and put in the necessary work to take control of it.

What can we do to “treat” a low BMR?

  • Exercise, exercise, exercise. Increasing LBM is the best and most established way to improve the BMR. That means not just doing cardio, but also doing RESISTANCE training to increase muscle mass. This can be challenging if you are not very comfortable in the gym or if you have pre-existing orthopedic problems. That makes it crucial to start slow, work with a qualified professional, do it safely, and progress only with supervision.
  • High Intensity Interval Training (HIIT). HIIT has been proposed as a great form of exercise to improve BMR (please see my pervious post on HIIT here ). Specifically, people cite the EPOC, or essentially the body’s increased burning of calories even after you have completed the exercise. While this is true, HIIT does burn more calories after you exercise when compared to cardio exercise, the absolute number is small. In addition, when comparing 20min of HIIT to 45 minutes of moderate cardio exercise, the total calories burned tends to favor the moderate exercise. That does not mean you should avoid HIIT. Absolutely not! It is a fantastic form of exercise for improved fitness and increased LBM. However it is also easy to overstate its effect on BMR.
  • Green tea and Spicy foods- Technically these do improve your BMR. However, they only improve it by about 4%, and only for 30-60 minutes after ingesting the food. Not much bang for your buck.
  • Testosterone- Even in people without “low T.” testosterone supplementation can increase BMR by approximately 10%. This is felt to mostly be due to the increased LBM, and less due to some intrinsic effect of testosterone itself. I don’t want to get into the whole topic of testosterone supplementation (that is a whole blog or two in itself), but increasing LBM and BMR does seem to provide two more reasons for making sure if you have low T you should be evaluated, treated and monitored.
  • Definitely fallen out of favor due to side effects and complications.

What are other strategies?

  • Increase the percentage of active metabolism. Remember in the beginning I mentioned that BMR accounts for 60-70% of our daily energy expenditure. Thermogenesis is roughly 10% and active metabolism is the rest. One of the best things we can do is increase the time we are doing active metabolism! That obviously includes regular exercise, but also simple things like taking the stairs instead of the elevator, parking far away from your office or the shopping mall, getting up and walking around the office every 30-60 minutes. As our society becomes more of a sitting society, this needs to be more of a constant reminder.
  • Make sure weight loss strategies also include LBM maintenance strategies. Many “crash diets” work well for weight loss, but at the expense of losing muscle mass. Guess what that does to the BMR….lowers it further! So even though you lost weight, you also lost LBM, lowered your BMR, and you made it that much more likely that you will gain the weight back with your newly reduced BMR.

What about eating 6 small meals every day? This is one of the most popular beliefs about improving your BMR. The problem is that the science does not support it. The theory is that by providing a relatively constant supply of food for your body to break down, you are keeping the metabolic rate going and preventing it from shutting down. However, the work to digest 3000kcal is actually the same whether you ingest it as 500 kcal 6 times per day or 1500 kcal twice per day. That is not to say that frequent small meals are not a good weight loss technique. It works great for some people. But it does not work by increasing your BMR. It works because for some people it helps cut down on feeling hungry and the inevitable cravings that can lead to binge eating, usually on simple carbohydrate snacks. So if that works for you, Great! But be warry of the “calorie creep.” Sometimes as people get used to eating frequent small meals, the meals start to become not-so-small and the calories increase. Also, it forces people to think about food more, search for food more, and plan ahead to make sure you are surrounded by good food choices. If you need to eat every 3 hours, you better be good at avoiding the chips, cookies, muffins, and other poor choices that are far too plentiful in most work settings.

But doesn’t eating less frequently cause your body to shut down metabolism to preserve energy? This is likely only the case if you fast for 72hours or more. If you remember my previous post I talked about intermittent fasting with a 7hr feeding cycle and 17hour fasting cycle ( . This works well for weight loss in most people and does not slow BMR. It doesn’t work for everyone, but if you can stick to the schedule, it can be very effective. Please see that post for more details.

In summary, our metabolism does slow as we age. But the good news is that we can control it! There is no magic bullet to fix it, but by making healthy nutritional choices, increasing our resistance training, and being more active during the day, we can increase our daily energy expenditures. So when someone says to me, “Doc, I just can’t lose the weight. I have always had a slow metabolism and it has just gotten worse with age.” I know that part of his statement may be true, but I also know that most of it is still under your control. At Boundless Health, it is our priority to educate you about the facts, and develop an individualized program that will give you the highest chance of succeeding. Therein lies the art of individualized medicine that we make a priority at Boundless Health. Contact us today to learn more!

0 replies

Leave a Reply

Want to join the discussion?
Feel free to contribute!

Leave a Reply

Your email address will not be published. Required fields are marked *